Jan H. Näsman

Stabilization of poly(l-lactide) in the melt

The purpose of this study was to investigate the thermal degradation of poly(l-lactide) and to develop a stabilizer. The melt degradation of poly(l-lactide) was studied in the temperature range 180–220°C using a melt rheometer for monitoring changes in the melt viscosity. Further studies of the degraded PLLA were made using SEC, 1H-NMR and DSC. The thermal degradation was found to proceed by random main-chain scission. The mechanisms include depolymerization and oxidative degradation in the presence of oxygen. However, hydrolysis as well as intermolecular and intramolecular reactions could not be excluded. Benzoyl peroxide was found to stabilize the polymer against thermal degradation by deactivating the catalyst residues. The melting point of the stabilized polymer decreased with increasing peroxide concentration.

Structural investigation of radiation grafted and sulfonated poly(vinylidene fluoride), PVDF, membranes

Radiation grafted and sulfonated poly(vinylidene fluoride), PVDF, membranes have been studied by thermal analysis and X-ray diffraction to determine the changes in membrane crystallinity and structure during preparation. Commercial PVDF films were irradiated with an electron beam, grafted with styrene and finally sulfonated. Both the crystallinity and the size of the crystallites of PVDF decrease in the grafting reaction. A further decrease in crystallinity is observed in the sulfonation reaction. The residual crystallinity of PVDF was considerable (10–20%) even in membranes which had been subjected to severe reaction conditions. These results can be explained by assuming that the grafting takes place mainly in the amorphous region of the PVDF, and close to the surfaces of the crystals, but that grafts do not penetrate into the crystals. The proton conductivity of the grafted and sulfonated PVDF membranes reached values comparable to those of Nafion membranes.

Structure and properties of sulfonated poly [(vinylidene fluoride)–g-styrene] norous membranes porous membranes

The possibility of developing polyfvinylidene fluoride (PVDF)-based membranes as proton conductors has been investigated. Using electron beam radiation grafting and functionalisation, the composition of the membranes can be controlled. Membranes have been prepared from porous films of PVDF, and their structure and properties have been studied with Raman spectroscopy, wide angle X-ray scattering (WAXS), small angle X-ray scattering (SAXS), swelling tests, and by impedance spectroscopy. The grafting reaction of styrene, initiated in the amorphous regions and at the surfaces of the crystallites in the partly crystalline PVDF matrix, is very efficient, and high degrees of grafting can be achieved. Grafts are formed both from C–H and C–F branch pointsl Sulfonation can be accomplished to ca. 100%, and occurs mainly at the para-position of the phenyl rings. The hydration number was found to be independent of the degree of grafting, degree of sulfonation and crystallinity. The overall crystallinity decreased in the structure with the degree of grafting and sulfonation, partly owing to the diluting effect of the grafts, partly owing to efficient penetration of the grafts in the crystallites. The conductivity increased with the content of sulfonic acid groups and, in particular, with decreasing crystallinity. In the case of fully sulfonated membranes, a levelling-out of the conductivity was found at a degree of grafting of around 200%. Conductivities up to 120 mS cm–1 at room temperature were achieved.

Synthesis and properties of sulfonated and crosslinked poly[(vinylidene fluoride)-graft-styrene] membranes

Crosslinked proton exchange membranes were prepared by electron beam grafting of styrene with divinylbenzene, DVB, or bis(vinyl phenyl)ethane, BVPE, on to poly(vinylidene fluoride), PVDF, followed by sulfonation. The area and thickness increase, crystallinity and mechanical properties of the membranes were investigated. All these properties were influenced by the crosslinker structure and its concentration. The crosslinkers increase the final degree of grafting. For noncrosslinked membranes it was about 80% and with 10% of BVPE crosslinker about 180% after 8 hr. The area increase with grafting is very similar for the noncrosslinked membranes and the differently crosslinked membranes, but the crosslinkers reduce swelling for sulfonated membranes swelled in boiling water. DVB reduces swelling more than BVPE. With grafting, the crystallinity of the PVDF phase decreases; with 10% BVPE the decrease is smallest and with 10% DVB largest. The mechanical properties of the sulfonated swelled membranes decrease with the degree of grafting, for a 10% DVB crosslinked membrane the strength decreases to zero at degrees of grafting higher than 75%.

Phase separation and crystallinity in proton conducting membranes of styrene grafted and sulfonated poly(vinylidene fluoride)

A series of proton exchange membranes have been prepared by the preirradiation grafting method. Styrene was grafted onto a matrix of poly(vinylidene fluoride) (PVDF) after electron beam irradiation. Part of the samples was crosslinked with divinylbenzene (DVB) or bis(vinylphenyl)ethane (BVPE). Subsequent sulfonation gave membranes grafted with poly(styrene sulfonic acid) and marked PVDF-g-PSSA. It was found that the intrinsic crystallinity of the matrix decreased in both the grafting and the sulfonation reaction in all the membranes. The graft penetration and the ion conductivity are influenced strongly by the crosslinker. The ion conductivity is considerably lower in crosslinked membranes than in noncrosslinked ones. Generally, the mechanical strength decreases with crosslinking. The membranes show a regular phase separated structure in which the sulfonated grafts are incorporated in the amorphous parts of the matrix polymer. The phase separated domains are small, of the order of magnitude of 100–250 nm. These were resolved on transmission electron micrographs and on atomic force images but could not be resolved with microprobe Raman spectroscopy.

Hydrolytic degradation of peroxide modified poly(L-lactide)

Abstract Poly(L-lactide) (PLLA) was prepared by a tin(II)-octanoate initiated ring-opening polymerization in the melt and separately melt modified with tert -butylperoxy benzoate (0.1, 0.25 and 0.5 wt%) in order to deactivate the residual tin compounds and reduce melt degradation. Injection molded specimens of unmodified and peroxide-modified PLLA were prepared for a hydrolytic degradation study, where the changes in the weight, mechanical strength, molar mass and morphology were studied during the immersion in buffer solutions (pH 7.4) at 37 °C. The hydrolytic degradation of both the unmodified and the peroxide-modified PLLA was rapid. This was found to depend on the residual dilactide content, which in all samples was above 11% before the immersion. The peroxide modified samples underwent a more rapid hydrolytic degradation than the unmodified ones, which can be related to the morphological changes caused by the peroxide modification.

Transport of drugs across porous ion exchange membranes

Porous ion exchange membranes have potential applications for drug delivery systems. Permeability of these membranes can be controlled by environmental factors like pH and ionic strength but also the drug properties have an important role in the permeation process. In this paper the influence of the drug charge, lipophilicity and molecular weight on the diffusional drug flux is demonstrated. The membranes under study were poly(acrylic acid) (PAA) grafted porous poly(vinylidene fluoride) (PVDF) membranes which are cation selective due to the partial ionization of carboxyl groups in grafted PAA chains. At low pH the membrane pores are open and the drugs can diffuse through the membrane quite easily. However, at pH 7 the grafted chains partially block the pores and the diffusional flux of bigger drug molecules (Mw9400) decreases five orders of magnitude and also the flux of smaller molecules is clearly reduced. When the influence of the drug charge on the diffusion of the drugs across the membranes was studied, it turned out that the PAA-PVDF membranes facilitate the transport of cationic drugs and repel anionic ones. The presented mathematical model, based on Donnan drugs equilibrium and measured transport number data, predicted the observed trends reasonably well.

Drug permeation through a temperature-sensitive poly(N- isopropylacrylamide) grafted poly(vinylidene fluoride) membrane

Abstract Poly( N -isopropylacrylamide) (poly(NIPAAm)) is a temperature sensitive polymer, which has been used in the development of thermally controlled devices. In the present study, poly(NIPAA)m grafted poly(vinylidene fluoride) (PVDF) membranes were prepared by an irradiation method and fluxes of model compounds across the various grafted membranes were measured. The effectiveness of various grafted membranes to control drug fluxes by temperature was studied using FITC-dextrans (molecular weights 4400–50 600) and mannitol as model compounds. Also, the effect of environmental conditions on the LCST of the membrane was evaluated. The fluxes of bigger molecules across a temperature sensitive, porous poly(NIPAA)m–PVDF membranes were effectively controlled by temperature, environmental ionic strength and degree of grafting of the membrane, while flux of the smaller molecules was not controlled thermally even at high degree of membrane grafting. These result indicates that the studied membranes are useful in controlling the permeation of high molecular weight compounds such as polynucleotides, peptides and proteins.

Copolymerization of ethene with 1-hexene or 1-hexadecene over ethylene, dimethylsilylene and 1,4-butanediylsilylene bridged bis(indenyl) and bis(tetrahydroindenyl) zirconium dichlorides

Ethene was copolymerized with 1-hexene and 1-hexadecene over five different homogeneous methylaluminoxane (MAO) activated racemic ansa-metallocene catalysts in order to study both the influence of the ligand (indenyl and tetrahydroindenyl) and the influence of the interannular bridge (ethylene, dimethylsilylene and 1.4.-butanediylsilylene) on the copolymerization behaviour. Hydrogenation of the indenyl ligands was found to decrease comonomer content and molar mass of the copolymers. A similar tendency was observed for the ethylene bridge compared to the silylene bridges. The reasons for this behaviour are discussed and related to structural differences of the catalyst precursors. In addition a segregation fractionation technique was applied to study the chemical composition distribution (CCD) of the produced copolymers. Batchwise feed of comonomer resulted in a broad CCD. More homogeneous copolymers could be produced using partly continuous feed of comonomer.

Tetramethyldiamido phosphate directed β-lithiation of a π-excessive heterocycle; d2-synthon to 2-substituted butenolides

Abstract The tetramethyldiamido phosphate group is described as a novel and tetracoordinated directing group in a reliable and synthetically useful β-lithiation of furan 1 . Addition of 1.1 equiv. n-BuLi to 1 and quenching with electrophiles gave 2,3-disubstituted furans 3 . In 98–100 % formic acid 3 is converted to 4 in good overall yield. Thus furyltetramethyldiamido phosphate 1 is a d 2 -synthon for 2-furanone.